Field of the Invention
The present invention relates to a water splitting catalyst, and a method for producing oxygen and hydrogen using the same.
Related Background Art
Water is the most abundant electron source present in nature, and can be said as an important chemical resource playing roles in producing oxygen and hydrogen by proton reduction, and in synthesizing a substance by carbon dioxide reduction. Nevertheless, it is only noble metals such as iridium and ruthenium that are known as catalysts excellent in a reaction for artificially acquiring electrons from water, that is, oxygen generation reaction (2H2O→O2+4H++4e−) (S. Trasatti, G. Buzzanca, J. Electroanal. Chem., 1971, 29, A1. A. Harriman, I. J. Pickering, J. M. Thomas, P. A. Christensen, J. Chem. Soc., Faraday Trans. 1, 1988, 84, 2795. Yixin Zhao, Nella M. Vargas-Barbosa, Emil A. Hernandez-Pagan and Thomas E. Mallouk, small 2011, 7(14), 2087). The development of catalyst materials made of 3d-block transition metal elements present abundantly has been desired.
Manganese is the only 3d-block transition metal element that catalyzes oxygen generation in nature. In photosynthetic photosystem II (photochemical system II complex, PSII), a Mn4-cluster exhibits high catalyst activity and substrate selectivity in an oxidation reaction of water. Accordingly, as a design guideline for obtaining a catalyst capable of efficiently oxidizing water, an approach has been adopted for mimicking the structure of a Mn4-cluster (Kanady J S, Tsui E Y, Day M W, Agapie T., Science. 2011 Aug. 5; 333(6043):733-6. Brimblecombe R., Swiegers G. F., Dismukes G. C., Spiccia L., Angew Chem Int Ed, 2008, 47, 7335-7338).
However, many artificial manganese catalysts mimicking the structure have a low activity, and require a large energy application to drive the reaction particularly within a neutral range. As a result, an artificial photosynthetic system utilizing such a manganese catalyst has a problem of very low energy conversion efficiencies in producing oxygen and hydrogen, and in utilizing carbon dioxide as a resource.